1. Field of the Invention
The invention relates to an ink cartridge for supplying ink to an ink jet printer which performs recording by ejecting ink droplets onto a recording medium such as a recording sheet, and more particularly to an ink cartridge having an ink holding member for holding ink within a multiplicity of pores.
2. Description of Related Art
Generally, an ink jet printer for recording on a recording sheet by ejecting ink droplets has, within the body case, an ink jet recording head; a recording device for replaceably mounting an ink cartridge thereon which contains ink for being supplied to the recording head; a conveying device for conveying a recording sheet; and a carriage device for reciprocating the recording device in accordance with the size of the recording medium conveyed by the conveying device. The conveying device is structured to rotationally drive a platen roller whose axis extends in parallel to the reciprocating direction of the recording device so as to convey the recording medium in a direction perpendicular to the reciprocating direction of the recording device. The carriage device is structured to support the carriage, on which the recording device is mounted, so as to permit it to slide on a guide rod, which extends in parallel to the platen roller's axis, and to cause the carriage to reciprocate in the axis direction of the platen roller by means of a belt tensioned around a driving pulley driven by a motor and a driven pulley.
In the recording device, such as the ink jet printer as described above, an ink cartridge is used which holds predetermined color, amount and/or type ink for supplying ink to the recording device. Also, a porous ink holding member, such as sponge and urethane foam, is placed in the ink cartridge. The urethane foam which has been widely used has an unstable ink mobility due to the capillary phenomenon because of a large variation in pore density. In order to solve this problem, the urethane foam has, to date, been compressed for use. When the urethane foam is compressed, pores having large diameters are easily compressed and the density of the pores will be averaged.
Also, it is necessary that the ink holding member is closely placed in the inner wall surface of the ink cartridge. For example, a perspective view of a hollow cartridge body used for a conventional ink cartridge is shown in FIG. 13. In FIG. 13, the cartridge body 32 is shaped like a rectangular parallelepiped with its upper portion opened, and has a round ink outlet 34 at the lower portion, its inner side corner lines 31A, 31B, 31C and 31D, and 33A, 33B, 33C and 33D being substantially orthogonal respectively.
The ink cartridge is manufactured as described below. An ink holding member 16 (see FIG. 2) shaped like a rectangular parallelepiped for holding ink therein is manufactured slightly larger than the internal space of the cartridge body 32 and the ink holding member 16 is compressed to be inserted into the cartridge body 32. Thereafter, a lid is placed on the open side, which is opposite to the ink outlet 34, and ink is poured through an ink filling port provided on the lid. The ink holding member 16 is manufactured to satisfy the condition of W2&gt;W3, D2&gt;D3 and H2&gt;H3 as compared with the internal space of the cartridge body 32 (FIG. 13) in order to bring it into tight contact with the inner wall surface 35 of the cartridge body 32.
FIG. 14 is a cross-sectional view showing an ink cartridge composed of the cartridge body 32 and the ink holding member 16. The ink contained in the ink holding member 16 flows out of the ink outlet 34 due to the capillary phenomenon, and is supplied to the ink jet head through an ink passage provided within the printer.
The conventional ink cartridge has, however, had the following problem. Being larger than the internal space of the cartridge body 32, the ink holding member 16 must be inserted into the cartridge body 32 by being forcibly compressed when the ink holding member 16 is inserted into the cartridge body 32. Since a frictional force is generated between the ink holding member 16 and the cartridge body 32 at this time, the ink holding member 16 is not pressed with a tight contact with the inner wall surface 35 of the cartridge body 32, and therefore, strain occurs in the ink holding member 16. Further, in the corner portions 31A, 31B, 31C and 31D, the ink holding member 16 receives frictional forces from two adjacent planes, and since the frictional forces are not uniform, strains easily occur in the ink holding member 16 in the corner portions 31A, 31B, 31C and 31D. As a result, there are portions where the ink holding member 16 and the cartridge body 32 are not brought into tight contact, that is, gaps occur. Particularly, as shown in FIG. 14, the gaps 38 easily occur in the corner portions 31A, 31B, 31C and 31D. Since the gaps 38 thus formed are as fine as several tens of microns, it is very difficult to closely insert the ink holding member 16 into the cartridge body 32.
Further, in another type of ink cartridge, as shown in FIGS. 15 and 16, an ink holding member 51 is inserted into a hollow cartridge body 52 from an opening provided on the upper portion, and the opening is closed with a lid member 53 in the same manner as the ink cartridge shown in FIGS. 13 and 14. In addition, the cartridge body 52 is formed with an ink supply port 54 for supplying ink to the recording head, and an air conductive hole 55 for maintaining the internal space at the atmospheric pressure and making smooth the supply of ink to the recording head through the ink supply port 54.
In the case of such a structure, the ink cartridge is generally manufactured by blocking an opening with the lid member 53 for solvent welding after the cartridge body 52 is filled with ink through the opening in a state in which the ink holding member 51 has been compressed Therefore, the compression force which is exerted on the ink holding member 51 is released after the completion of solvent welding of the lid member 53, the ink holding member 51 intends to expand and return to the original state for filling the entire interior of the ink cartridge. However, the surface of the lid member 53 which is brought into contact with the ink holding member 51 is flat, and the connecting portion between the lid member 53 and the cartridge body 52 is square. Therefore, the ink holding member 51 which has expanded and returned to the original state does not align with the shape of the connecting portion, and gaps 56 (a portion of lower density than other portions) are formed between the ink holding member 51 and the lid member 53. Also, gaps 56 easily occur at the circumferential edge portion of the ink holding member 51 in contact with the cartridge body 52 because it is more difficult to expand and return to the original state than in the central portion because of the friction between the peripheral edge portion and the wall surface.
When such gaps 38, 56 as described above are formed, air will be mixed in the flow of ink within the ink holding member 16, 51, thus making it impossible to stably supply ink to the ink jet head. Therefore, mottle or blur will occur upon a printing operation and further, in the worse case, printing becomes impossible.
Also, when such gaps 38, 56 as described above are formed, ink first flows out along the gaps 38, 56 during ink distributed pouring to cause the ink holding member 16, 51 to absorb ink. And, ink is not uniformly distributed in the entire ink holding member 16, 51, but defectively distributed so that pouring easily occurs. Also, when air is fed to the printing head through the gaps 38, 56 it becomes impossible to accurately eject ink, or even to eject ink from the printing head. In addition, when the gaps 38, 56 are formed, air flows in through the gaps 38, 56, and the complete use of ink also cannot be effected well.